Abstract To investigate the influence of vertical zonation permeability characteristics of water-rich karst on external water pressure in deep-buried long-distance water conveyance tunnels, the Fenjie river valley section of the Yunkai Mountain Tunnel in the Beibu Gulf Guangdong Water Resources Allocation Project was selected as the study site. A novel borehole water pressure testing device was developed to conduct stratified hydraulic connection measurements, revealing the permeability characteristics between upper and lower rock layers above the tunnel and enabling vertical zoning of the overlying rock mass. Results indicate that the overlying rock mass of the valley section can be vertically divided into a modern karst layer, a middle enhanced karst layer, and a deep isolated karst void layer. The lower boundary of the modern karst layer is approximately 100 m, the middle enhanced karst layer
extends down to about 160 m, and the tunnel is located within the deep isolated karst void layer, approximately 30 m away from the bottom of the middle enhanced karst layer. Based on this, numerical simulations were conducted to compare the effects of vertical zonation permeability and homogeneous permeability on external water pressure.Compared with the homogeneous seepage model, the seepage modele considering karst vertical zonging eliminates the funnel-shaped pore pressure contour distribution due to variations in permeability within rock layers. The maximum and minimum external water pressures occur at the tunnel crown (7.13 × 10? Pa) and invert arch(7.07 × 10?Pa), respectively. The maximum external water pressure in the vertically zoned seepage model reaches 231.5% of that predicted by the homogeneous seepage model.
Abstract：
To investigate the influence of vertical zonation permeability characteristics of water-rich karst on external water pressure in deep-buried long-distance water conveyance tunnels, the Fenjie river valley section of the Yunkai Mountain Tunnel in the Beibu Gulf Guangdong Water Resources Allocation Project was selected as the study site. A novel borehole water pressure testing device was developed to conduct stratified hydraulic connection measurements, revealing the permeability characteristics between upper and lower rock layers above the tunnel and enabling vertical zoning of the overlying rock mass. Results indicate that the overlying rock mass of the valley section can be vertically divided into a modern karst layer, a middle enhanced karst layer, and a deep isolated karst void layer. The lower boundary of the modern karst layer is approximately 100 m, the middle enhanced karst layer
extends down to about 160 m, and the tunnel is located within the deep isolated karst void layer, approximately 30 m away from the bottom of the middle enhanced karst layer. Based on this, numerical simulations were conducted to compare the effects of vertical zonation permeability and homogeneous permeability on external water pressure.Compared with the homogeneous seepage model, the seepage modele considering karst vertical zonging eliminates the funnel-shaped pore pressure contour distribution due to variations in permeability within rock layers. The maximum and minimum external water pressures occur at the tunnel crown (7.13 × 10? Pa) and invert arch(7.07 × 10?Pa), respectively. The maximum external water pressure in the vertically zoned seepage model reaches 231.5% of that predicted by the homogeneous seepage model.
LI Zhensong1 GUO Qinghua2 ZHANG Ning1 HE rongjian2 ZHANG Xiaoping1 ZHANG Haoran1
.Influence of Permeability Characteristics of Vertical Zonation in Water-rich
Karst on External Water Pressure of Tunnels[J] MODERN TUNNELLING TECHNOLOGY, 2025,V62(4): 37-49
2025, Vol. 62 